Hydrostatic transaxle having axial piston motor and method for manufacturing transaxles

ABSTRACT

A modular hydrostatic transaxle includes an axle module removably connected to a hydrostatic transmission module. The axle module includes a differential connected to a reduction gear train and disposed in an axle casing. A pair of axles are connected to the differential and supported within the axle casing. The hydrostatic transmission module comprises a transmission casing separate from the axle casing and hydraulically connected pump and motor disposed in the transmission casing. The motor output connection includes a shaft piloted to an input drive of the reduction gear train, which constitutes the alignment mechanism of the transmission and axle modules. The pump and motor cylinder barrels are hydraulically connected through the pump and motor block at 90° orientation, and a portion of the pump and motor block forms an inclined surface which supports a face of a thrust bearing. At least one homogeneous low friction bearing strip is confined between the swash plate and the interior portion of the casing. A disconnect mechanism includes a spring that urges a sleeve to engage the output and input shafts. The brake disc is disposed on a distal end of the output shaft and a brake cover is fastened to the outer portion of the axle casing and substantially encloses the brake disc.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to and claims the benefit under 35U.S.C. § 119(e) of U.S. Provisional Applications No. 60/119,381 filedFeb. 9, 1999, and 60/145,619 filed Jul. 26, 1999.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to hydrostatic transaxles intendedprimarily for use in the lawn and garden industry on riding lawnmowers,lawn and garden tractors and the like, but may also be applied to largerimplements and vehicles.

[0003] Hydrostatic transmissions transmit rotary mechanical motion,typically from an internal combustion engine, to fluid motion, typicallyoil, and then back to rotary mechanical motion to rotate a pair of driveaxles in order to drive the vehicle. The hydrostatic transmissioncontrols the output rotary mechanical motion such that varying outputspeeds in the forward and reverse directions are possible with a singlespeed input rotary mechanical motion. Such transmissions have utilizedradial piston pumps and motors, axial piston pumps and motors and hybridtransmissions wherein the pump may be of the radial piston design, forexample, and motor formed as a gear pump. The speed of the output of thetransmission is typically controlled by varying the eccentricity of thepump track ring or swash plate.

[0004] In recent years, and particularly for smaller displacementapplications, it has been common practice to integrate the hydrostatictransmission within the axle casing that also contains the differentialand bearings for the two axles. Such casings are typically split along ahorizontal plane containing the axis of the axles, and the casing itselfis formed of only two parts. However, it is also known to utilizecasings comprising three or more components wherein the casingcomponents are attached to each other along vertical split lines orhorizontal and vertical split lines.

[0005] Although utilizing a single casing for both the transmission andaxle gear components necessitates only two large die castings, there arecertain disadvantages inherent in such a design. One such disadvantageis that servicing of the hydrostatic transmission or the geartrain/differential requires that the entire casing be opened, the oildrained and the complete mechanism withdrawn in order to perform suchservice. Furthermore, units wherein the hydrostatic transmission issized for different displacements, for example, use with larger lawn andgarden tractors, will require completely different transaxle casings.Since such casings are quite large and require expensive tooling tomanufacture, this represents a significant additional cost. Furthermore,integrated hydrostatic transaxles are often noisy, especially whenaccelerating.

[0006] A typical construction of the hydrostatic transmission componentof the transaxle includes a one-piece block common to both the pump andmotor units, often referred to as a “center section.” The center sectionfacilitates an external mounting surface for a motor barrel and a pumpbarrel, and additionally, an internal valve body for providing hydrauliccommunication between the pump and motor barrels. Conventionally, thepump and motor barrel axes of rotation are 90 degrees to one another.Center section machining is difficult because the center section issubstantial in size and machined surfaces are substantiallyperpendicular, often requiring multiaxis machining capabilities. Thiscorresponds to a significant cost associated with this design type.

[0007] Moreover, many HSTs heretofore require that the pump and motormechanism unit be matched to a fixed swash plate prior to mounting themechanism into the casing. Typically, assembly requires positioning thefixed swash plate in the casing, mounting the pump and motor mechanisminto the casing then taking measures to ensure the fixed swash plate issuitably aligned with the pump and motor mechanism. Arranging the fixedswash plate and pump and motor mechanism, in the manner described above,poses a significant step in the assembly process which representsadditional cost.

SUMMARY OF THE INVENTION

[0008] The present invention is a modular transaxle providing an axlemodule including an axle casing, a differential and a reduction geartrain connected to a differential. The differential and gear train aredisposed in the axle casing and a pair of axles are connected to thedifferential and supported within the axle casing. A hydrostatictransmission module comprising a transmission casing separate from theaxle casing hydraulically connects a pump and motor disposed in thetransmission casing. An input drives the pump and the motor has anoutput connection to drivingly connected the reduction gear train to themotor. The hydrostatic transmission casing is removably connected to theaxle mechanism casing. The motor output connection includes a shaftpiloted to an input drive of the reduction gear train. The piloting ofthe shaft and input drive constitutes the alignment mechanism of thetransmission and axle modules.

[0009] The present invention further provides a hydrostatic transmissionincluding an axle module having a casing, a differential and a reductiongear train connected to the differential. The differential and geartrain are provided in the axle casing and a pair of axles are connectedto the differential and are supported within the casing. A hydrostatictransmission module comprises a casing separate from the axle modulecasing and includes a hydraulically connected pump and motor within thetransmission casing. The pump has an input for driving the pump and themotor has an output connection attaching the reduction gear train to themotor. The hydrostatic transmission casing is connected to the axlecasing and the motor output connection includes a shaft attaching to aninput drive of the reduction gear train. The hydrostatic transmissionmodule includes a pump and motor block rotatably supporting a pumpcylinder barrel and a motor cylinder barrel. The pump and motor cylinderbarrels are hydraulically connected through the pump and motor block andinclude axes of rotations substantially 90° offset. A portion of thepump and motor block forms an inclined surface which supports one faceof a thrust bearing. The other face of the thrust bearing is engagedwith a plurality of reciprocal pistons in the motor cylinder barrel.

[0010] In one form of the invention, the axle casing has two majorcasing halves joined together at an interface, the casing halves aresubstantially mirror images relative to one another about the interface.

[0011] A swash plate is positioned between the pistons and an interiorportion of the transmission casing and preferably at least onehomogeneous low friction bearing strip is confined between the swashplate and the interior portion of the casing.

[0012] A disconnect mechanism removably connects the axle module withthe hydrostatic transmission and is disposed within the differentialcasing. The disconnect mechanism include a sleeve, a lever and aresilient member. The output shaft is selectively engaged with the inputshaft through the sleeve and the resilient member urges the sleeve toengage the output and input shafts.

[0013] A brake shaft having an end disposed within the axle casing ismeshingly coupled to the reduction gearing and preferably includes apair of friction pads sandwiching a brake disc. The brake disc isdisposed on the other end of the brake shaft and provided externally ofthe axle casing. A brake cover is fastened to the outer portion of theaxle casing and substantially encloses the brake disc.

[0014] The present invention further provides a transaxle system and amethod for manufacturing transaxles in either the left hand controlledor right hand controlled configurations using substantially identicalaxle modules. The transmission module used in the left hand controlledtransaxle has the transmission module having the output shaft on theleft and the control lever on the right when viewing the transmissioncasing with the pulley upwardly directed and toward the rear of thecasing. On the other hand, the transmission module used in the righthand controlled transaxle has the transmission module having the outputshaft on the right and the control lever on the left when viewing thetransmission casing with the pulley upwardly directed and toward therear of the casing. The use of either the left hand controlled or righthand controlled hydrostatic transmission modules allows either the lefthand controlled hydrostatic transaxle or right hand hydrostatictransaxle configurations to be constructed using identicallymanufactured axle modules that are inverted for left or right handdrives.

[0015] The modular arrangement enables the hydrostatic transmission tobe quickly removed and a replacement unit bolted in place if thehydrostatic transmission requires repair. The transmission can be sentback to the factory for rebuilding, and only minimal downtime to theconsumer's lawn and garden vehicle will be experienced.

[0016] Another advantage to the modular approach is that a variety ofhydrostatic transmissions and a variety of axle mechanisms can be mixedand matched to meet customers' application requirements.

[0017] A further advantage is that the use of a separate casing forenclosing the hydrostatic transmission enables the hydraulic componentsto be much more tightly held in place, thereby reducing noise, which isa problem with many integrated transaxles wherein the single casingencloses both the transmission and reduction gearing/differentialmechanisms.

[0018] In the particular embodiment disclosed herein, the hydrostatictransmission employs an axial piston pump having a vertical input shaft,and an axial piston motor having a horizontal output shaft that extendsout of the transmission casing and engages the reduction gear train ofthe axle mechanism through a mechanical disconnect device.

[0019] A further improvement in the transaxle of the present inventionis the use of a brake cover, which may be made of molded plastic, inorder to protect the brake disc from debris.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above-mentioned and other features and objects of thisinvention, and the manner of attaining them, will become more apparentand the invention itself will be better understood by reference to thefollowing description of the embodiments of the invention taken inconjunction with the accompanying drawings, wherein:

[0021]FIG. 1 is a sectional view of the left hand controlled transaxleof the present invention taken along a horizontal plane intersecting theaxes of the axles;

[0022]FIG. 2 is a sectional view of the left hand controlled hydrostatictransmission taken along a vertical plane;

[0023]FIG. 3 is a top sectional view of the brake mechanism;

[0024]FIG. 4 is a vertical sectional view of the brake mechanism;

[0025]FIG. 5 is an enlarged sectional view of the hydrostatictransmission illustrating the pump;

[0026]FIG. 6 is a plan view of the center section for the hydrostatictransmission;

[0027]FIG. 7 is an elevational view of the center section;

[0028]FIG. 8 is a perspective view of the center section viewed from thebottom;

[0029]FIG. 9 is a perspective view of the center section viewed from thetop;

[0030]FIG. 10 is a sectional view of the reduction gearing anddifferential module taken along a horizontal plane coincident with theaxes of the axles and wherein the hydrostatic transmission module hasbeen disconnected therefrom;

[0031]FIG. 11 is an elevational view partially in section showing asecond, fender shift embodiment of the hydrostatic transmission;

[0032]FIG. 12 is a sectional view of the fender shift embodiment;

[0033]FIG. 13 is a sectional view taken along a horizontal plane of thesecond embodiment;

[0034]FIG. 14 is an exploded view of the pump and motor assembly of thesecond embodiment of the hydrostatic transmission;

[0035]FIG. 15 is a sectional view taken along line 15-15 of FIG. 14 andviewed in the direction of the arrows;

[0036]FIG. 16 is a perspective view of the motor block for the secondembodiment;

[0037]FIG. 17 is a sectional view of FIG. 16 taken along line 17-17 andviewed in the direction of the arrows;

[0038]FIG. 18 is a bottom view of the motor block;

[0039]FIG. 19 is a bottom view of the upper half casing of thehydrostatic transmission broken away showing one of the bearing strips;

[0040]FIG. 20 is an end elevation of one of the bearing strips;

[0041]FIG. 21 is an end view of the swash block; and

[0042]FIG. 22 is a front elevation of the swash block.

[0043]FIG. 23 is a sectional view of the pump block and thrust bearingtaken along a vertical plane showing retainment of the thrust bearing;

[0044]FIG. 24 is an elevated front view of the pump block and thrustbearing assembly of FIG. 23;

[0045]FIG. 25 is a perspective of the left hand controlled transaxle;

[0046]FIG. 26 is a top plan view of the transaxle of FIG. 25 partiallybroken away showing the hydrostatic transmission module removed from theaxle module;

[0047]FIG. 27 is a top plan view of a right hand controlled transaxlepartially broken away showing the hydrostatic transmission moduleremoved from the axle module;

[0048]FIG. 28 is an elevational view of the left hand controlledtransaxle of FIG. 25 showing the transmission module removed; and

[0049]FIG. 29 is an elevational view of the right hand controlledtransaxle of FIG. 27 showing the transmission module removed.

DETAILED DESCRIPTION OF THE INVENTION

[0050] Referring to FIG. 25, there is shown left hand controlledhydrostatic transaxle 8 including hydrostatic transmission module 10fastened to axle module 12. Hydrostatic transaxle 8 receives power froma power source (not shown), typically an internal combustion engine, andprovides controllable power to axles 20 and 22 which drive wheelsattached thereto (not shown). Axle module 12 is provided with aplurality of bolt holes 13 through its structure to secure the unit tothe frame (not shown) of an agricultural vehicle or other like receivingstructure utilizing transaxle 8. Power is transferred from the powersource to transaxle 8 typically by a belt (not shown) engaged withpulley 199 attached to transaxle 8. External controls provided withtransaxle 8 include brake lever 70 and control lever 202. Control lever202 provides control of both speed and direction of the transaxle 8.

[0051] Referring to FIG. 26, the piloting and coupling structure whichprovides attachment between axle and hydrostatic transmission modules12, 10 of left hand controlled transaxle 8 will be discussed.Hydrostatic transmission module 10 is drivingly coupled to axle module12 through bore or inner surface 210 provided within end 43 of outputshaft 26 which extends from transmission 10 and is coaxially engagedwith outer surface 47 of end 152 of gear train input shaft 32. Inputshaft end 152 is recessed within clearance hole 49 provided in axlecasing 18. Shaft end 152 extends outwardly from and without anyinterference of casing 78 to provide uninterfered mating of shafts 26and 32 and allows alignment of axle and transmission modules 12,exclusively by engagement of shaft ends 43 and 152. Bolt receiving holes57 provided in transmission casing 78 provide radial clearance for apair of bolts (not shown) to extend through and engage with a pair ofthreaded holes 59 provided in mounting elements or bosses 154, 156provided in axle casing 18. Thus, the bolts act to secure transmissionmodule 10 to axle module 12 and do not assist in alignment. Note thatoutput shaft 26, rotatably supported within transmission casing 78,includes radial ‘play’ relative to axle casing 18 to further facilitateproper engagement and non-binding operation between axle module 12 andhydrostatic transmission module 10. Sleeve 148 of sleeve and bearingassembly 150 is press fit into transmission casing 78 and includes anextended portion 149 external to casing 149 which extends into acircular recessed portion 151 (FIG. 10) of axle casing 18 (FIGS. 1 and13). However, a clearance 153 (FIG. 1) exists between extended portion149 of sleeve 148 and recessed portion 151 of axle casing 18 soalignment of axle module 12 and transmission module is provided solelyby shafts 26 and 32. The piloting and mounting of right hand controlledtransmission module 11 to axle module 12 to form transaxle 9 (FIG. 27)is identical to the piloting and mounting of left hand controlledtransmission 10 to axle module 12 to form transaxle 8 (FIG. 26).

[0052] Referring now to FIG. 1, left hand hydrostatic transaxle 8comprises a hydrostatic transmission module 10 and an axle module 12,the latter including reduction gear train 14 and differential mechanism16. Axle module 12 includes a casing 18 formed of upper and lower halves21, 25 respectively, only upper casing half 21 is shown here, whereincasing halves 21, 25 are split along a horizontal plane or parting line33 coincident with the axes of axles 20 and 22 (FIGS. 1, 28-29). Axles20 and 22 extend outwardly from differential 16 through openings in theends of casing 18, which are sealed by means of seals 23, and whereinaxles 20 and 22 are supported by bearings 24.

[0053] The output shaft 26 from the motor 138 of hydrostatictransmission module 10 extends into a space 28 which carries amechanical disconnect mechanism 30 of the type disclosed in U.S. Pat.No. 5,701,738 assigned to the assignee of the present application. Thispatent is expressly incorporated herein by reference. The disconnectmechanism 30 comprises a splined sleeve 31 that is moved axially bylever 19 (FIG. 10) to connect and disconnect shafts 26 and 32. Outputshaft 26 is piloted around gear train input shaft 32 and shaft 32 issupported by bearings 36 and 38 (FIGS. 1 and 10). Shaft 32 is sealed byseals 40 and 42. Splined to shaft 32 is pinion gear 44, which is inintermeshing engagement with gear 46 splined to countershaft 48. Pinion50, which is also splined to countershaft 48, engages ring gear 52 ofdifferential 16. Differential 16 comprises pin 54 that carries bevelgears 56 and further comprises bevel gears 58 splined to axles 20 and22. Reduction gear train 14 reduces the rotational speed of output shaft32 and transmits the rotational motion to differential 16, which rotatesaxles 20 and 22 in a known manner. Axle casing 18 is filled with anappropriate lubricating oil or grease, and the entire casing is sealedfrom the ambient by seals 40, 42 and 23.

[0054] Referring now to FIGS. 1, 3 and 4, brake mechanism 60 will bedescribed. The distal end 62 of shaft 32 is splined to disc 64 which isengaged by a pair of friction pads 66 (FIG. 4), wherein one of thefriction pads 66 is pressed against disc 64 by a pair of pins 68(FIG. 1) when brake lever 70 is rotated. A cast housing 76 supports thebrake mechanism 60 and is mounted to axle casing by a pair of screws.Brake mechanism 60 employs a self-adjustment feature comprising aself-adjusting nut 72 that accommodates friction pad wear. The operationof the brake itself is well known and the self-adjustment mechanism isthe subject of co-pending patent application Ser. No. 09/165,904, filedOct. 2, 1998, and assigned to the assignee of the present application.This application is expressly incorporated herein by reference.

[0055] A further feature of brake mechanism 60 is the provision of aplastic injection molded cover 74 that attaches to the cast housing 76,and prevents grass clippings, dirt and other debris from fouling thebrake mechanism (FIG. 25). Referring to FIGS. 3 and 4, brake cover 74includes enclosure portion 75 and flange 77. A pair of apertures 79 areprovided in flange 77 which receive a pair of screws 81 to fasten cover74 to a pair of threaded holes 83 in cast housing 76.

[0056] Referring to FIGS. 2 and 5, hydrostatic transmission module 10comprises a separate, self-contained casing 78 having two casing halves80 and 82 split along a horizontal interface 84 that is coplanar withthe axis of motor output shaft 26 (FIG. 1). Casing halves 80 and 82 areconnected together by means of a plurality of screws 86 (FIG. 5) thatextend through the lower casing half 82 and are threadedly received inbores in the upper casing half 80. Disposed within casing 78 is ahydrostatic pump and motor mechanism 88 comprising center section 90having a pump mounting surface 92 (FIG. 5) and a motor mounting surface94 (FIG. 9) and internal passages 96 and 98 (FIG. 6) hydraulicallyconnecting arcuate slots 100 and 102 in pump face 92 with arcuate slots112 and 114, respectively, in motor mounting face 94 (FIG. 9). As bestseen in FIGS. 6 and 7, arrows 104 illustrate fluid circulation throughcenter section 90. Note that fluid circulation may be reversed, relativeto the direction indicated by direction 104, by rotating control arm 202(FIG. 5) to tilt swash plate 130 (FIG. 2). Swash plate 130 includes abidirectional range of tilt indicated by arrows 106 (FIG. 2).

[0057] Referring to FIG. 5, pump cylinder barrel 116, splined to inputshaft 118 includes a plurality of chambers 120 in which are disposedpistons 122 urged against swash plate assembly 127 by means of springs126. The swash plate assembly 127 includes a pair of races or groovedplates 124, 125 separated by a plurality of ball bearings 128 providedin a swash plate 130. Shaft 118 is sealed within upper casing half 80 bymeans of seal 132 and rotatably supported by bearings 134 and 136. Notethat pump shaft 118 extends through swash plate assembly 127 and issplined to pump cylinder barrel 116. The distal end of shaft 118 issupported by bearing 136 in center section 90. Screws 87 connect centersection 90 to upper casing half 80 (FIGS. 2 and 5).

[0058] Referring now to FIGS. 1 and 2, axial piston motor 138 comprisesa rotatable cylinder barrel 140 having a plurality of pistons 142therein that rotate against fixed swash plate assembly 144, whereincylinder barrel 140 is rotatably mounted on the face 94 (FIG. 9) ofcenter section 90. Motor output shaft 26 extends through cylinder 140and is supported by means of bearing 146 in center section 90 (FIG. 1).The axis of output shaft 26 is horizontal and oriented 90° relative topump input shaft 118. Referring to FIGS. 1 and 13, motor output shaft 26is supported by means of sleeve and bearing assembly 150 that is pressfit into casing 78 and sleeve 148 of sleeve and bearing assembly 150extends into recessed portion 151 in axle casing 18. Sleeve 148 includesan extended portion 149 which is superposed by recessed portion 151 ofaxle casing, however, extended portion 149 and recessed portion ofcasing 18 are separated by a clearance 153 such that output shaft 26 isat no time confined by axle casing 18. Piloting of transmission module10 with gear train 14 is accomplished by means of surface 47 of areduced end 152 of gearing input shaft 32 being received within an innersurface or bore 210 of an end 43 of motor output shaft 26 (FIGS. 1,26-27). Because transmission casing 78 is not directly piloted to axlecasing 18, binding of shafts 26 and 32 is avoided. Casing 78 is mountedto casing 18 at two locations 154 and 156 (FIGS. 1, 26-27) by means ofoverlapping extensions or bosses on casings 78 and 18 and bolts (notshown) that fasten from the bottom. These mounting points resist therotational torque between transmission module 10 and gear mechanism 12.

[0059] Referring now to FIGS. 5-9, the lower surface 158 of centersection 90 is provided with a pair of openings 160 to provide makeup oilto pump cylinder barrel 116, and a filter (not shown) and check valves(not shown) will be provided as is customary. Pump shaft 118 providedwith bearing 136 (FIG. 5) is received within bore 162. Integral bosses164 of center section 90 accommodate and provide support for themounting screws 87. Blind drilled passageways will be sealed by plugs270 as is customary in the art. Center section 90 includes an extendedportion or bearing cradle 184 to support bearing assembly or thrustbearing 186 (FIG. 1) therein. Bearing cradle 184 includes a clearancehole 188 to allow motor shaft 26 to extend through and spline to motorcylinder barrel 140 (FIG. 1).

[0060] As shown in FIG. 2, pump swash plate assembly 127 will be tiltedthrough the range 106 provided by the action of control rod 166 andcontrol arm 168 (FIG. 5) in order to vary the displacement of pump 169.

[0061]FIG. 10 is a further view of the gear train 14 and differentialmechanism 16 wherein hydrostatic transmission module 10 has beendisconnected therefrom. Shown more clearly is the reduced end 152 ofinput shaft 32 on which output shaft 26 of transmission module 10 ispiloted. As described previously, because both transmission module 10and axle module 12 are modular, axle module 12 can be reversed in orderto provide right hand or left hand connections to brake 60 and the inputshaft 118 of transmission module 10. For example, to provide aconnection which is reversed to that shown in FIG. 1, one would invertaxle module 12 about a horizontal axis perpendicular to axles 20 and 22and mount a modified right hand (or left hand) mirror image transmissionmodule 9 (FIG. 27) thereto in the same fashion as shown in FIG. 1 but onthe opposite side of the gear reduction drive train portion of axlemodule 12. This enables right hand and left hand drives to be providedto a customer base with the need to stock only two hydrostatictransmission modules 9, 10 and a single axle module 12.

[0062] FIGS. 11-18 illustrate a modified embodiment of transmissionmodule 10 wherein certain corresponding elements are denoted by primedreference numerals. In this embodiment, one-piece center section 90 isnot used. In its place is pump and Is motor mechanism 88′ including pumpvalve body or pump block 170 and motor block 172 (FIG. 14). Pump andmotor mechanism 88′ provides the valving for motor cylinder barrel 140to hydraulically connect with pump cylinder barrel through transferpassages 96′ and 98′. Motor block 172 is fastened to pump block 170 toform pump and motor block 173. Motor block 172 is fastened to pump block170 by means of screws 87 that extend through bores 176 in motor block172 and holes 178 in pump block 170 (FIGS. 2, 14, 16 and 18). Pump block170 and motor block 172 are mounted to upper casing half 80′ by means offastening screws 87 (FIGS. 2, 5 and 12) that pass through openings 180and 182 (FIGS. 13-15).

[0063] Pump block 170 includes a fixed swash plate support face orbearing cradle 184 (FIGS. 13, 14, 23 and 24) that is disposed at a fixedangle α (FIG. 23) relative to the horizontal plane Y and carries ballbearing assembly or thrust bearing 186 (FIGS. 14, 23 and 24) againstwhich motor pistons 142 rotate thereby causing motor cylinder barrel 140to rotate and drive output shaft 26. Opening on clearance hole 188passing through bearing cradle 184 provides clearance for output shaft26. Makeup oil to hydrostatic transmission module 10′ is providedthrough ports 160 having check valves, similar to ports and check valvesin center section 90, as shown in FIG. 8.

[0064] Motor block 172 is provided with a pair of ports 192 and 194 thatalign with ports 174 in pump block 170 in order to provide hydrauliccommunication between the arcuate slots 112′ and 114′ in the face 94′ ofmotor block 172 through transfer passages 96′ and 98′ to the arcuateslots 102′ and 100′ in the face 92′ against which pump cylinder barrel116 (FIG. 12) rotates. Motor block 172 includes bore 196 which supportsrotatable end 254 of output shaft 26. Alternatively, end 254 of outputshaft 26 includes a bearing fitted thereon which fits into bore 196 tosuitably support rotatable shaft end 254.

[0065] Referring now to FIG. 12, it will be seen that pump input shaft118 is driven by means of a pulley 199 driven by a belt connected to asimilar pulley (not shown) on the output shaft of an internal combustionengine (not shown), for example. Pulley 199 forms an assembly with fan198 supported on a common hub 200 that is keyed to shaft 118. FIGS. 11and 12 illustrate a fender shift version of the unit wherein control arm168 is rotated by shaft 166, the latter rotated by means of shift lever202 fastened to shaft 166 by screw 204. A friction pack comprising apair of friction pucks 205 grip shift lever 202 to retain lever 202 inthe position set by the operator. Clamping force on friction pucks 205is accomplished by means of a spring 207 disposed on stud 209, thelatter being slidably received in upper casing half 80′. In a foot pedalversion (FIG. 5) the corresponding shift lever 202 is returned toneutral by means of a conventional return-to-neutral spring mechanism203. On the foot pedal version shown in FIG. 5, adjustable plate 207permits fine adjustment of neutral position.

[0066]FIG. 13 illustrates motor 138′ in greater detail and it will beseen that output shaft 26 is supported by bearing 206 and is sealedagainst casing 80′, 82′ by sleeve 148 of sleeve and bearing assembly 150and oil seal 208. The bore 210 in the end of shaft 26 pilots around end152 of input shaft 32 of axle module 12 (FIG. 10), and axial compressionspring 212 maintains splined sleeve 31 of the mechanical disconnectmechanism (FIG. 10) engaged with the splined portion 211 of shaft 32when motor output shaft 26 is inserted into axle module 12. Axialcompression spring 212 is coaxially arranged about output shaft 26(FIGS. 1, 5, 12, 13, 26 and 27) and confined between splined sleeve 31and retaining ring 213 (FIG. 1). Retaining ring 213 is engaged or‘snapped’ in groove 221 formed in output shaft 26 as is customary. Aflat washer 223 may be provided between retaining ring and compressionspring 212 to provide further support for compression spring 212. Inoperation, as disconnect lever 19 is rotated clockwise as viewed in FIG.10, sleeve 31 is moved axially to the left against the pressure ofspring 212. This very simple mechanism eliminates the need for anexternal spring or torsion spring on other elements typical of externaldisconnect mechanisms. Preferably, spring 212 is a Smalley flat wiremetal spring. Output shaft 26 is rotated by cylinder barrel 140 of motor138 and extends through clearance opening 188 in bearing cradle 184.

[0067] As shown in FIGS. 2, 5 and 12, swash plate 130 includes a pair ofarcuate upper surfaces 214 (FIGS. 21 and 22) that bear against a pair ofarcuate bearing strips 216 (FIGS. 19 and 20) that are fastened intorecessed area 215 of upper casing half (80, 80′). Bearing strips 216 aremade of TEFLON impregnated DELRIN and swash plate 130 is preferably madeof carbon steel by means of a powder metal process. Specifically,bearing strips 216 may be manufactured by, for example, a plasticinjection molding process comprising a homogeneous composition of DELRINand about 20% PTFE. Openings 217 (FIGS. 19 and 20) in each of thebearing strips 216 are engaged by a cast protrusion 219 on the internalwall 215 of upper casing 80, 80′ (FIG. 19). Concave recessed area 215 ofupper casing half 80, 80′ defines a pair of concave surfaces 218 each ofwhich contact a convex outer surface 220 (FIGS. 2 and 20) of eachbearing strip 216. Each bearing strip 216 includes a concave innersurface 222 (FIGS. 2, 19 and 20) in contact with each respective arcuateupper surface 214 of swash plate 130. Referring to FIGS. 5 and 12, acompression force created by springs 126 urging pump pistons 122 againstswash plate assembly 127, presses swash plate 130 against bearing strips216 to correspondingly hold each bearing strip 216 against surface 218of casing (80, 80′). Each cast protrusion 219 is integrally formedwithin upper half casing 80, 80′ and projects from surface 218. Eachprojection extends into opening 217 of each bearing strip 216 to preventmovement of bearing strips 216 during tilting of swash plate 130.Referring to FIGS. 2, 5, 11 and 12, displacement of lever 202 urgesswash plate 130 to swing in an arc defined by the curvature of convexsurfaces 218 within upper casing half (80, 80′). Bearing strips 216 areflexible and thereby partially deform to the curvature of upper halfcasing surfaces 218, and additionally to arcuate swash plate surfaces214. Since bearing strips 216 deform to abutting surfaces, minimal ifany machining of these surfaces is required. Because bearing stripscomprise a homogeneous material rather than merely a coating on a metalstrip, they will exhibit better wear and a longer life.

[0068] Referring to FIG. 12, shown is hydrostatic transmission module 10of transaxle 8, including pump and motor mechanism 88′ comprising pump169′, motor 138′, and pump and motor block assembly 173 (FIG. 3). Pumpand motor block assembly 173 includes a two piece structure wherein pumpblock 170 is joined with motor block 172 to provide a single integratedunit (FIG. 14). Rotatably supported by pump and motor block assembly 173is pump cylinder barrel 116 and motor cylinder barrel 140 (FIG. 3). Pumpcylinder barrel 116 includes a plurality of axially arranged chambers120 having pistons 122 disposed in each chamber 120. Typically, pumpcylinder barrel 116 and pistons 122 are common and interchangeable withmotor cylinder barrel 140 and pistons 142 to decrease costs associatedwith implementing separate components. Springs 126 are provided withineach chamber 120 and contact pistons 122 to urge pistons 122 toward andagainst swash plate assembly 127. Thrust bearing 186 is coaxial relativeto pump cylinder barrel 116, and in contact with outermost extents ofpistons 122. Thrust bearing 186 fits snugly within swash block or swashplate 130, specifically plate 124 of thrust bearing 186 engages bore 224(FIGS. 5 and 12) of swash plate 130. A counterbore (not shown), iscoaxial with bore 224 and is positioned adjacent plate 125 of thrustbearing 186 to provide rotational clearance for plate 125 of thrustbearing 186 to rotate freely within swash plate 130.

[0069] Operation of hydrostatic pump and motor mechanism 88′, throughmovement of swash plate 130 to effectuate variable rotational movementof the motor cylinder barrel 140, will now be described. Customarily,pump cylinder barrel 116 is driven by the power source through inputshaft 118. Typically, input shaft 118 includes a first end attached topulley 199 and pulley 199 is belt driven by the power source (notshown). The other end of input shaft 118 includes a splined portion 226disposed on the surface of input shaft 118 and engages matching splinedportion 228 formed within pump cylinder barrel 116. Swash plate 130,selectively controlled by shift lever 202, which is external to thehydrostatic transmission casing, initiates fluid displacement withinpump cylinder barrel 116 to transfer power from input shaft 118 to driveaxles 20, 22. Neutral switch 119 is provided on an external surface oftransmission casing 78 and extends through the casing to register off ofa periphery of the swash plate 130 (FIG. 5). Neutral switch 119 is inelectrical communication with a vehicle's ignition switch (not shown) toprevent vehicle start-up when the hydrostatic transmission is engaged.Shift lever 202 is attached to rotatable control arm 168 by screw 204,external of casing (78, 78′). Control arm 166 includes first end 230attached to control rod 166 and a second end 232 extending outwardly andgenerally perpendicular from control rod 166. Second end 232 of controlarm 166 swings through an arc respective of control rod 166 when controlrod 166 is rotated. Pin 234 attaches to second end 232 of control arm166 and extends into slot 236 disposed on periphery 238 (FIGS. 21 and22) of swash plate 130. Friction roller 240 fits over pin 234 and freelyrotates about pin 234 to engage with slot 236 of swash plate 130.Selectively positioning control lever 202, typically by an operatordepressing a foot pedal linked thereto through linkage means, causesswash plate 130 to tilt, and in turn, pistons 122, orbiting about inputshaft 118, reciprocate causing fluid in each cylinder 120 to pressurizeas the respective piston retracts. Swash plate 130 tilts and rotatesagainst a pair of low friction bearings attached to the casing aspreviously described.

[0070] Referring to FIG. 14, pump and motor block assembly 173 includespump block 170 and motor block 172 joined together by screws 87. Pumpblock 170 includes cylindrical portion 242 joining rectangular bodyportion 244. Raised circular face 92′ is disposed on cylindrical portion242 and constitutes a mounting surface for pump cylinder barrel 116.Rectangular body portion 244 of pump block 170 includes a raisedrectangular motor block mounting surface 246 which provides a surface toattach motor block 172. A pair of annular column portions or bosses 248,250 are joined to pump block 170 and each include fasteners 87 extendingthrough to fasten the pump and motor block assembly 173 to upper casinghalf 80′ (FIGS. 12 and 13). A projecting semi-circular bearing cradle184, to provide a seat for fixed thrust bearing 186, is integral withbody portion 244 of pump block 170. Bearing cradle 184 includes anannular face 252 which is substantially smooth and flat in the “as-cast”condition, thus this surface requires little if any machining. The pumpblock 170 may be constructed of an aluminum alloy and fabricated by, forexample, a foam insert casting process. Annular face 252 is inclined atangle α, respective of vertical reference plane Y (FIG. 1), to suitablycause motor pistons 142 to reciprocate, within chambers 120. Preferably,α is 15°. Clearance hole or opening 188 is generally centered in face252 of bearing cradle 184 and end 254 of output shaft 26 extends throughclearance hole 188 and attaches to motor cylinder barrel 140 (FIG. 14).Hole 256 is threaded and disposed in a lower portion of inclined face252 to receive stop member 258 which constitutes, for example, a screwto retain thrust bearing 186 as shown in FIG. 23.

[0071] Motor block 172 includes mounting surface 260 (FIGS. 17 and 18)which overlays block mounting surface 246 of rectangular portion 244 ofpump block 170. Referring to FIGS. 6-9, motor block 172 includes a pairof circular fluid ports 192, 194 positioned between a pair of outerfastener clearance holes 176, which respectively align with and overlayrespectively, the pair of circular fluid ports 174 and the pair of outerholes 178 within pump block 170 (FIG. 14). Screws 87 extend throughrespective clearance holes 176 within motor block 172 and intorespective holes 178 within pump block 170. Motor block 172 includesraised circular mounting face 94′, which is substantially perpendicularto block mounting surface 260, to which motor cylinder barrel 140 isrotatingly mounted. As best seen in FIG. 14, a pair of inserts 262, 264made of powered metal are interference fit around screws 87 and betweenpump and motor blocks 170, 172 to suitably seal and align fluid ports192, 194 of pump block 170 with fluid ports 174 of motor block 172.

[0072] Referring to FIG. 15, the pair of hydraulic passages internal topump block 170 will be described. Pump block 170 includes arcuateopenings 100′, 102′ in face 92′ which extend within an interior ofcylindrical portion 242 of pump block 170 and respectively intercept thetransfer passages 96′, 98′ disposed within rectangular portion 244 ofpump block 170. Passages 96′, 98′ may include as-cast arcuate wallsdefining the passageways extending from pump mount face 92′ torespective fluid ports 174, by being formed through, for example, a foaminsert casting process. Alternatively, passages 96′, 98′ may be machinedto include entrance holes 266, 268 respectively capped by threaded plugs270 (FIG. 24).

[0073] Referring to FIGS. 16-18, the hydraulic passages within motorblock 172 will be described. Motor block 172 includes arcuate slots112′, 114′ provided in face 94 which extend inwardly and intersect ports192, 194. Referring to FIGS. 16 and 17, motor mount face 94′ alsoincludes centered bore 196 extending substantially perpendicular to face94′ and which provides support for rotating output shaft 26 extendingthrough motor cylinder barrel 140 to align motor cylinder barrel 140 onface 94′. Motor block 172 may be formed by, for example, a powder metalprocess, which provides suitable smooth and continuous walls definingcontinuous arcuate slots 112′, 114′ intersecting ports 192, 194. Thus,motor block 172, joined to pump block 170 comprising pump and motorblock assembly 173, provides two complete and continuous passagesextending from pump mount face 92′ to motor mount face 94.

[0074] Referring to FIG. 14, typically, pump cylinder barrel 116 isdriven by input shaft 118 and face 276 of pump cylinder barrel 116 abutsface 92′ of pump block 170. Similarly arranged is face of motor cylinderbarrel 140 against face 94 of motor cylinder block 172. Face 276 of pumpcylinder barrel 116 includes a plurality of axial arranged ports 280(FIGS. 5 and 12) through which hydraulic fluid communicates from pistonchamber 120 to arcuate slots 110′ and 112′. Similarly, face 278 of motorcylinder barrel 140 includes a plurality of axial arranged ports 280(FIGS. 1, 13 and 14) through which hydraulic fluid communicates frommotor cylinder chambers 120 to arcuate slots 112′, 114′. Thus, thecylinder barrels must be in close proximity with the arcuate orificesdisposed in the motor and pump blocks to sustain a suitable hydraulicconnection between the pump and motor during operation. It is desirableto retain an amount of pressurized fluid disposed between each barrelface and the block mount face, often referred to as “floating” thebarrel. Floating provides a dynamic seal and contemporaneously reducesfriction between the cylinder barrel and respective mount face duringoperation of the pump and motor mechanism.

[0075] As best seen in FIGS. 5 and 12, pump cylinder barrel 116 alignswith face 92 of pump block 170 due to end 282 of input shaft 118 beingguided by a bearing fitted within bore 162 in pump block 170.Alternatively, bore 162 may include a solid press fit bearing tosuitably support shaft 118. Bore 162 is generally centered about face92′ of pump block 170, and as best shown in FIGS. 14-15, bore 162includes slot 284 axially positioned along the length of thereof. Inoperation, slot 284 allows excess oil to return to lower casing half82′, and additionally, acts as a hydraulic pressure relief. Otherwise,the quantity of oil trapped beneath cylinder barrel face 276 tends to“lift” cylinder barrel 116 excessively away from pump mount face 92′resulting in a detrimental loss of hydraulic pressure in the system anda corresponding loss of system efficiency. Similarly, and as best seenin FIGS. 16 and 17, bore 196 in face 94′ of motor block 172 includesslot 286 to relieve excessive hydraulic pressure between motor barrel140 and face 94′ of motor block 172.

[0076] Referring to FIGS. 6, 7, 9, 13, 14, 23 and 24, shown is bearingcradle 184 integral with pump block 244 of pump and motor mechanism 88′.Bearing cradle 184 is arranged oppositely respective of face 184 ofmotor block 172. In operation, motor barrel 140 rotates about motormount face 94′ and pistons 142, within each chamber 120, displace fluiddependant on the tilt of thrust bearing 186. The outermost extent 288 ofeach piston 142 contacts first plate 124 of thrust bearing 186 creatinga ring of contact, preferably centered on thrust bearing 186 to providea substantially uniform distribution of force through thrust bearing186.

[0077] Referring to FIGS. 23 and 24, the arrangement between thrustbearing 186 and bearing cradle 186 will be described. Thrust bearing186, includes the pair of annular plates 124, 125, a plurality of ballbearings 128 between the plates and retaining ring 290 to retain ballbearings 128 therein. Customarily, plates 124 and 125 of thrust bearing186 have similar inner surface 242 dimensions and a similar outersurface 294 dimension. In operation, plate 124 contacts annular face 252of bearing cradle 184, remaining substantially stationary, while plate125 rotates as outermost extents 288 of pistons 142 are urged againstplate 125. Thrust bearing 186, and specifically plate 124, is restrainedfrom downward and side to side movement by a raised semi-circularshoulder portion 296 of bearing cradle 184 (FIGS. 13, 14, and 24).Additionally, thrust bearing 186 is restrained from movement in anupward direction, along annular face 252, by stop member 258. Stopmember 258 is a stationary threaded fastener having outer head portion298 contacting inner surface 292 of plate 124 of thrust member 186. Stopmember 258 threads into threaded hole 256 within bearing cradle 184(FIGS. 13, 14, and 24). Hole 256 extends into bearing cradle 184 and isgenerally axially aligned with pistons 142 in motor barrel 140. Stopmember 258 lockingly engages threaded hole 256 so that the stop membercan be threaded to a suitable depth and thereafter sustain a stationaryposition so that operational vibration will not affect stop memberposition. Retaining bearing 186 in this manner eases assembly andreduces cost.

[0078] The present invention hydrostatic transaxle 8 is “modular”meaning common axle module 12 connected to left-hand hydrostatictransmission 10 defines left-hand controlled transaxle 8, as shown inFIG. 25. Alternatively, by inverting common axle module 12 and attachingright hand controlled hydrostatic transmission 11, right hand controlledtransaxle 9 is formed (FIG. 27). Right hand transaxle 9 operatesidentically to left hand transaxle 8 and transaxle 9 differs only inorientation, i.e., the brake handle is on the left and the control leveris on the right. Common axle module 12, readily adaptable-to twoalternate transmissions, significantly increases a manufacture's productline without a concomitant increase in the number of stocked components.

[0079] Referring to FIGS. 26 and 28, left-hand controlled transaxle 8includes axle casing 18 and transmission casing 78. Axle casing 18defines two substantially mirror image casing halves 21, 25 fastenedtogether by a plurality of bolts 15 (FIG. 28). Referring to FIGS. 25, 26and 28, each casing half 21, 25 includes respective stiffening ribs 27,35 and gusset 29 to provide suitable support and stiffness to supportaxles 20, 22, reduction gearing and differential mechanism (FIGS. 1 and10). In operation, axles and 22 are exposed to significant levels ofstress and torque common to the rigorous usage and loading of typicalagricultural usage of transaxle 8. Therefore, each casing half 21, 25comprising suitably stiff axle casing 18, is provided with gusset 29integrally formed with respective stiffening ribs 27, 35. As best seenin FIG. 28, left hand controlled transaxle 8 possesses symmetry relativeto casing parting line 33. Specifically, stiffening ribs 27 and gusset29 on casing half 21 is a mirror image of stiffening ribs 35 and gusset29 on casing half 25. Additionally, the size and placement of gusset 29on casing half 21 is a mirror image of the size and placement of gusset29 provided on casing half 25 relative to parting line 33. In a similarmanner, mounting bosses 39 on casing half 21 are mirror images ofmounting bosses 41 provided on casing half 25, relative to parting line33. Since right hand transaxle 9 (FIGS. 27 and 29) differs from lefthand transaxle 8 only in attachment of right hand hydrostatictransmission 11, axle module 12, and corresponding casing 18 areidentical in both transaxles 8 and 9.

[0080] Referring to FIGS. 26 and 27, the method for manufacturing aplurality of left hand controlled hydrostatic transaxles and a pluralityof right hand controlled hydrostatic transaxles, using the componentsdetailed above, will be described. In a production environment, it isdesirable to maintain and utilize an inventory of standardizedcomponents to thereby facilitate the manufacturing process and reduceexpenses associated with using different components. The presentinvention provides a method for using standardized components to produceleft hand and right hand controlled hydrostatic transaxles 8, 9respectively. The present method is particularly suitable forimplementation in a large scale production environment wherein it isdesired to quickly and efficiently produce numbers of left hand and/orright hand controlled hydrostatic transaxles and to be able to quicklyswitch over from producing one type of transaxle to another.

[0081] Using the method of the present invention, an inventory ofidentically manufactured axle modules 12 are used to quickly andefficiently produce a large number of left hand and/or right handcontrolled transaxles. Further, an inventory of left hand controlledhydrostatic transmission modules 10 and an inventory of right handcontrolled hydrostatic transmission modules 11 is provided for readyavailability and selection at the production facility. The availabilityof the inventory of identically manufactured axle modules 12, left handhydrostatic transmission modules 10 and right hand controlledhydrostatic transmission modules 11 at the production facility, allowsthe manufacturer to easily select and attach the required components toquickly and efficiently produce either a left hand controlled transaxle8 (FIG. 26) or a right hand controlled transaxle 9 (FIG. 27).

[0082] In order to produce a plurality of left hand controlledtransaxles 8, the manufacturer first provides axle modules 12 from theinventory of identically manufactured axle modules. Second, themanufacturer selects left hand controlled transmission module 10 fromthe inventory of left hand controlled transmission modules. Themanufacturer then attaches the selected components together to produce aplurality of left hand controlled transaxles 8. By continuouslyselecting axle modules and left hand controlled transmission modules andassembling the selected components, the manufacturer is able to quicklyand efficiently produce left hand controlled hydrostatic transaxles 8from the materials in the inventory.

[0083] When it is desired to produce a plurality of right handcontrolled hydrostatic transaxles 9, the manufacturer provides the axlemodule 12 from the inventory of identically manufactured axle modules 12and a plurality of right hand controlled transmission modules 11 fromthe inventory of right hand controlled transmission modules 11. Themanufacturer then assembles the selected components into a plurality ofright hand controlled transaxles 9. Again, by continuously selectingaxle modules 12 and right hand controlled hydrostatic transmissionmodules 11 in assembling the selected components, the manufacturer isable to easily and efficiently produce right hand controlled hydrostatictransaxles 9 from the materials in the inventory.

[0084] It can be seen that the manufacturer can switch from one type oftransaxle to another by simply selecting a different transmissionconfiguration while continuing to select the axle module from theinventory of identically manufactured axle modules. Therefore, the lefthand and right hand controlled hydrostatic transaxles can be easily andquickly assembled in large numbers. It can also be seen that asignificant cost reduction is possible due to the standardization of theaxle module thereby simplifying transaxle manufacturing and reducing theassociated costs.

[0085] While this invention has been described as having a preferreddesign, the present invention can be further modified within the spiritand scope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. A hydrostatic transaxle comprising: an axlemodule comprising an axle casing, a differential and a reduction geartrain connected to said differential, said gear train including an inputdrive, said differential and gear train disposed in said axle casing; apair of axles connected to said differential and supported within saidaxle casing; a hydrostatic transmission module comprising a transmissioncasing separate from said axle casing and a hydraulically connected pumpand motor disposed in said transmission casing, said pump having aninput driving said pump and said motor having an output means drivinglyconnected to said reduction gear train; said hydrostatic transmissioncasing removably connected to said axle mechanism casing; and said motoroutput means comprising a shaft piloted to said input drive of saidreduction gear train, the piloting of said shaft and input driveconstituting the alignment mechanism of said transmission and axlemodules.
 2. The hydrostatic transaxle of claim 1 wherein saidtransmission casing includes a pair of diametrically opposed mountingelements disposed on an external surface thereof which fixedly abut arespective pair of mounting elements on an external surface of said axlecasing.
 3. The hydrostatic transaxle of claim 1 wherein said motoroutput means comprises an output shaft and said input drive comprises aninput shaft, said output shaft defining a first surface coaxiallyengaged with a second surface defined by said input shaft, said outputshaft not radially confined by said axle casing, whereby the alignmentof said axle module with said transmission module consists solely ofengagement of said first and second surfaces of respective output andinput shafts.
 4. The hydrostatic transaxle of claim 1 wherein said axlecasing includes a recessed portion superimposed on a sleeve extendingfrom said transmission casing and rotatably supporting said motor outputmeans shaft, said sleeve and at least one of said transmission casingand said recessed portion separated by a clearance.
 5. The hydrostatictransaxle of claim 1 wherein said input drive of said reduction geartrain includes an input shaft having a distal end disposed externally ofsaid axle casing, said distal end of said input shaft attached to abrake disc, said brake disc being partially enclosed by a brake coverattached to said axle casing.
 6. The hydrostatic transaxle of claim 1,further comprising: a user operated mechanical disconnect mechanismdisposed intermediate the output means of said hydrostatic transmissionand said input drive of said reduction gear train; and said mechanicaldisconnect mechanism including an axially compressible spring associatedwith said output means to yieldably drivingly interconnect said outputmeans and said input drive when said modules are assembled to eachother.
 7. The hydrostatic transaxle of claim 6, wherein said outputmeans is selectively drivingly engaged to said input drive through acoupling sleeve, said compressible spring is captured between saidsleeve and said output means.
 8. The hydrostatic transaxle of claim 1,wherein said axle casing is substantially symmetrical about a planecoincident with an axis defined by said axles.
 9. The hydrostatictransaxle of claim 1, wherein said pump includes a tiltable swash plateand at least one low friction bearing strip is received in a concaverecess of said transmission casing and supports a portion of said swashplate.
 10. The hydrostatic transaxle of claim 9, wherein said at leastone bearing strip consists essentially of a homogenous flow of frictionmaterial.
 11. The hydrostatic transaxle of claim 1, wherein said axlecasing has a split line defined by a plane coincident with said axles,and said transmission casing has a split line defined by a planecoincident with an axis of said motor output means and parallel to saidaxle casing split line plane.
 12. A hydrostatic transaxle comprising: anaxle module comprising a casing, a differential and a reduction geartrain connected to said differential, said differential and gear traindisposed in said casing; a pair of axles connected to said differentialand supported within said casing; a hydrostatic transmission modulecomprising a casing separate from said axle module casing and ahydraulically connected pump and motor, said pump having an input fordriving said pump and said motor having an output means drivinglyconnected to said reduction gear train; said hydrostatic transmissioncasing connected to said axle casing; said motor output means comprisinga shaft connected to an input drive of said reduction gear train; andsaid hydrostatic transmission module including a pump and motor blockrotatably supporting a pump cylinder barrel and a motor cylinder barrel,said pump and motor cylinder barrels hydraulically connected throughsaid pump and motor block and include relative axes of rotation orientedsubstantially 90° relative to each other, a portion of said pump andmotor block forming an inclined surface which supports one face of athrust bearing, an opposite face of said thrust bearing engaged with aplurality of parallel pistons disposed in said motor cylinder barrel.13. The hydrostatic transaxle of claim 12 wherein said pump and motorblock comprises a motor block separable from and attached to a pumpblock defining a pair of continuous passages therein extendingrespectively and independently between said pump cylinder barrel andsaid motor cylinder barrel.
 14. A hydrostatic transaxle comprising: anaxle module having reduction gearing, a differential and a pair of axlesdisposed in an axle casing, said axle casing having two major casinghalves joined together at an interface, said casing halves aresubstantially symmetrical relative to one another about said interface;a hydrostatic transmission module including a pump and motor mechanismdisposed in a transmission casing, said transmission casing is removablyjoined to said axle casing and includes two major casing halves joinedat an interface; and a pump and motor mechanism disposed in saidtransmission casing and drivingly coupled to an output shaft, saidoutput shaft removably connected to said reduction gearing of said axlemodule.
 15. The transaxle of claim 14, wherein said interface of saidaxle casing defines a plane oriented parallel to said axles.
 16. Thetransaxle of claim 14, wherein said pump and motor mechanism is fastenedto one of said casing halves and includes an input shaft operablyconnected to said pump and motor mechanism, said input shaft extendsthrough said one of said casing halves.
 17. The transaxle of claim 14,wherein said output shaft of said hydrostatic transmission module iscoupled to said reduction gearing through a selectively disengageabledisconnect mechanism disposed in said axle module casing.
 18. Thetransaxle of claim 14, wherein said pump and motor mechanism comprises aswash plate disposed adjacent an interior surface of said hydrostatictransmission casing, at least one bearing strip mounted on said interiorsurface, and said swash plate tiltably engaged with said at least onebearing strip.
 19. The hydrostatic transaxle of claim 14, wherein saidtransmission module is a left hand drive module and said output shaftextends through a first side of said transmission casing in a left handorientation, and including an alternate right hand drive transmissionmodule having an output shaft that extends through a second side of saidright hand drive transmission module oriented 180° from the orientationof said left hand module, and said right hand module is alternativelydrivingly connectable to said axle module when said axle module isinverted about a horizontal axis perpendicular to said axles.
 20. Ahydrostatic transaxle comprising: a hydrostatic transmission casingdefining a hydrostatic transmission module and an axle unit includingreduction gearing meshingly coupled to a pair of axles through adifferential; a variable displacement pump disposed in said transmissioncasing including a pump cylinder barrel rotatably attached to a pumpblock, said cylinder barrel including a plurality of parallel, axiallydisposed cylinder chambers each having a reciprocating piston therein;an input shaft having an end drivingly connected to said cylinder barreland another end extending out through said transmission casing; a swashplate positioned between said pistons and an interior wall of saidtransmission casing, said swash plate selectively tiltable by means ofcontrol linkage attached to said swash plate; and at least onehomogeneous low friction bearing strip confined between said swash plateand said interior wall of said casing.
 21. The hydrostatic transaxle ofclaim 20, wherein said at least one homogeneous low friction bearingconstitutes a Delrin and Teflon composite.
 22. The hydrostatic transaxleof claim 20, wherein said low friction bearing includes an openingtherein and said bearing is fixed to said transmission casing by meansof a protuberance on said wall received in said opening.
 23. Thehydrostatic transaxle of claim 20, including two said bearing stripsthat engage a pair of arcuate surfaces on said swash plate.
 24. Ahydrostatic transaxle comprising: an axle module comprising an axlecasing, a differential and a reduction gear train, said gear trainincluding an input shaft, said differential and gear train disposed insaid axle casing; a pair of axles driven by said gear train andsupported within said axle casing; a hydrostatic transmission modulecomprising a transmission casing separate from said axle casing and ahydraulically connected pump and motor disposed within said transmissioncasing, said pump having an input driving said pump and said motorhaving an output shaft with an end thereof axially aligned with an endof said gear train input shaft, said hydrostatic transmission casingremovably connected to said axle mechanism casing; and a disconnectmechanism connecting said motor output shaft and said gear train inputshaft, said disconnect mechanism comprising: a sleeve slidably disposedon said ends of said shafts, said sleeve having a locked axial positionwhere it is rotationally locked to the ends of both said shafts and anunlocked axial position where it is rotationally locked to the end ofonly one of said shafts; a spring disposed around the end of one of saidshafts and positioned to yieldably urge said sleeve to the lockedposition when said transmission module is assembled to said axle module;and a user operated disconnect member that engages said sleeve.
 25. Thehydrostatic transaxle of claim 24 wherein said disconnect membercomprises a lever pivotably mounted to said axle casing.
 26. Thehydrostatic transaxle of claim 24, wherein said spring is a flat wirecompression spring coaxially arranged relative to said output shaft. 27.A hydrostatic transaxle comprising: an axle module having reductiongearing, a differential and a pair of axles disposed in an axle casing;a hydrostatic transmission module including a pump and motor mechanism;said pump and motor mechanism drivingly coupled to an output shaft, saidoutput shaft removably connected to said reduction gearing of said axlemodule; a brake shaft having an end disposed within said axle casing andcoupled to said reduction gearing; a brake mechanism including at leastone friction pad engaging a brake disc, said brake disc disposed on theother end of said brake shaft and disposed externally of said axlecasing; and a brake cover fastened to said axle casing and substantiallyenclosing said brake disc.
 28. The hydrostatic transaxle of claim 27,wherein said brake cover is molded plastic.
 29. A method ofmanufacturing a plurality of left hand controlled hydrostatic transaxlesand a plurality of right hand controlled hydrostatic transaxles,comprising the steps of: providing a plurality of substantiallyidentical axle modules; providing a plurality of left hand controlledhydrostatic transmission modules adapted to connect to respective axlemodules to form left hand controlled hydrostatic transaxles, and aplurality of right hand controlled hydrostatic transmission modulesadapted to connect to respective axle modules to form right handcontrolled hydrostatic transaxles; selecting a plurality of axle modulesfrom the plurality of axle modules and a plurality of left handcontrolled hydrostatic transmission modules; attaching the selected lefthand controlled hydrostatic transmission modules to the selected axlemodules to form a plurality of left hand controlled hydrostatictransaxles; selecting a second plurality of axle modules from theplurality of axle modules and a plurality of right hand controlledhydrostatic transmission modules; and attaching the selected right handcontrolled hydrostatic transmission modules to the selected axle modulesto form a plurality of right hand controlled hydrostatic transaxles. 30.A hydrostatic transaxle comprising: an axle unit comprising a casing, adifferential and a reduction gear train connected to said differential,said differential and gear train disposed in said casing; a pair ofaxles connected to said differential and supported within said casing; ahydrostatic transmission unit comprising a hydraulically connected pumpand motor, said pump having an input for driving said pump and saidmotor having an output means drivingly connected to said reduction geartrain; said motor output means comprising a shaft connected to an inputdrive of said reduction gear train; and said hydrostatic transmissionmodule including a pump and motor block rotatably supporting a pumpcylinder barrel and a motor cylinder barrel, said pump and motorcylinder barrels hydraulically connected through said pump and motorblock and include relative axes of rotation oriented substantially 90°relative to each other, a portion of said pump and motor block formingan inclined surface which supports one face of a thrust bearing, anopposite face of said thrust bearing engaged with a plurality ofparallel pistons disposed in said motor cylinder barrel.